To the average person, stock and broth might appear to be the same thing. They're both savory liquid and used as bases of sauces, soups and other dishes. However, there are three things that differentiate stock from broth: the ingredients, the cook time and the seasoning.
Broth is made by simmering meat, diced vegetables and aromatics (vegetables and spices added to the liquid to balance the flavor) in water. The cook time for broth is relatively short at only about two hours. Broth is almost always seasoned, so you can drink it on its own as well as use it for soups and sauces. Chicken broth is one of the more popular bases and is fairly simple to make at home.
If you're making vegetarian broth, the meat is substituted for other vegetables separate from the diced veggies. Common vegetables used in broths include carrots, celery, onions and tomatoes.
Unlike broth, stock is never seasoned. Stock is made by simmering diced vegetables, aromatics and bones in water -- while broth can contain bones, stock always does unless you're making a vegetarian stock recipe. Usually the bones are roasted before added to the water in order to make the stock richer in flavor. Stock also takes longer to prepare, usually from two to six hours, and is most often used in sauces, gravies, soups and stews.